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United States Patent |
5,172,983
|
Landrum
|
December 22, 1992
|
Eccentric rod bearing
Abstract
A connecting rod crankshaft bearing, provided for installation in the
connecting rod at the crankshaft end, eliminates the necessity for reaming
out the ridge in a cylinder during rebuilding. The rod bearing is an
eccentric bearing, provided as two semi-circular sections having a
slightly greater thickness along the lower section than on the upper
section so as to offset the center of the inner surface from the outer
surface of the bearing.
This offset restricts the uptravel of the connecting rod. This in turn
lowers the position of the piston during reciprocating travel by the same
amount, eliminating possible impact with wear ridges within the cylinder.
The cylinder thus need not be reamed to remove these ridges, as they no
longer present a source of damaging impact during piston travel.
Inventors:
|
Landrum; Anderson (Rte. 2. Box 311MM, Jackson, MS 39209)
|
Appl. No.:
|
652678 |
Filed:
|
February 6, 1991 |
Current U.S. Class: |
384/294; 123/48B; 384/255; 384/270 |
Intern'l Class: |
F16C 009/06; F16C 023/10; F02B 075/04 |
Field of Search: |
384/294,262,268,270,255,288,429,430
123/48 B
|
References Cited
U.S. Patent Documents
1987661 | Jan., 1935 | Blauvelt et al. | 123/48.
|
2542405 | Feb., 1951 | Fink | 384/270.
|
2897804 | Aug., 1959 | Crooks | 123/48.
|
3046953 | Jul., 1962 | Dolza | 384/294.
|
4073550 | Feb., 1978 | Yahraus | 384/294.
|
4084553 | Apr., 1978 | Forde et al. | 123/48.
|
4488826 | Dec., 1984 | Thompson | 384/288.
|
4864975 | Sep., 1989 | Hasegawa | 123/48.
|
Foreign Patent Documents |
696249 | Nov., 1979 | SU | 384/430.
|
1123827 | Nov., 1984 | SU | 384/429.
|
Primary Examiner: Hannon; Thomas R.
Attorney, Agent or Firm: Norcross; Alexander F.
Claims
I claim:
1. An improved reciprocating engine rod end bearing for replacement of a
used rod end bearing of standard design in a worn reciprocating engine
comprising:
a bearing having an inner cylinder surface defined by a first center and an
outer cylindrical surface defined by a second center;
said first center being offset from said second center by an amount
sufficient to lower the piston top dead center within the engine a
distance greater than a cylinder wear ridge length within the engine.
2. The bearing of claim 1 further comprising:
said bearing being formed of two semi-cylindrical sections;
means upon said semi-cylindrical sections for aligning said bearing within
a connecting rod.
3. A connecting rod end bearing for use in a worn reciprocating engine to
replace a worn rod end bearing of conventional design comprising:
a bearing for insertion within a connecting rod;
means within said bearing for lowering the top dead center position of a
piston operatively connected to said connecting rod whereby piston rings
on said piston will not contact a wear ridge within said worn engine.
4. The apparatus of claim 3 wherein said means for lowering further
comprises:
said bearing having an inner cylindrical surface defined by a first center
and an outer cylindrical surface defined by a second center;
said first center being offset from said second center;
said offset being substantially equal to the lowering of the top dead
center position;
said offset being substantially equal to or greater than several
thousandths inches.
5. The apparatus of claim 3 wherein said means for lowering further
comprises:
said bearing comprising an upper and a lower segment;
said lower segment being thicker than said upper segment by an offset;
said offset being equal to or greater than several thousandths inches.
6. An improved connecting rod end bearing, of the type having two facing
curved segments, for use in a reciprocating engine comprising:
said segments being an upper and a lower segment;
said segments defining an inner and an outer cylindrical surface;
said lower segment being thicker than said upper segment by an offset.
7. The apparatus of claim 6 further comprising:
said bearing aligned within an end of a connecting rod, said offset
lowering the top dead center position of a piston operatively connected to
said connecting rod.
Description
BACKGROUND OF THE INVENTION
This invention relates to the field of bearings for internal combustion
engine connecting rod.
As is known in the art internal combustion engines are generally
constructed in the form of a piston within a cylinder to form a combustion
chamber. The piston is in turn connected through a pivoted connecting rod
which is pivoted at an upper end to a pin in the piston and a lower end is
connected to an offset crank shaft rod journal.
The entire force of the engine is exerted through the connecting rod in
tension and compression against the crankshaft to be converted into rotary
engine motion. In order to reduce friction and resist the loads, a bearing
is then placed within the lower end of the connecting rod, where it
connects to the crankshaft. This bearing is lubricated with pressurized
oil through the crankshaft through internally provided oil passages within
the bearing, and the connecting rod in fact rides and pivots upon a thin
film of oil as the bearing is an otherwise high tolerance or tight fit,
required to avoid vibration, impact and slope and loss of power in
transferring the reciprocating motion of the piston into the rotary motion
of the crankshaft.
In order for the piston to function properly within the cylinder, it is
known that the piston is provided with certain compressed piston rings
lubricated by oil which is slung into the pistons and on the cylinder
walls by centrifugal force by rotation of the crankshaft rod throw as oil
is forced from between the rod journal and the rod bearing. This oil also
provides a gas tight seal permitting the development of adequate
compression, efficient burning, and transfer of the force generated by
expanding burned gas to the piston. These piston ring seals are vital to
the successful operation of a reciprocating engine and are deliberately
designed to absorb the frictional wear and the reciprocating motion of the
piston within the cylinder, as they may be readily replaced.
However, operation of the piston within the cylinder tends to wear the
cylinder walls where the piston rings travel. Thus, after a period of
usage of the engine, it will be found that the cylinder walls have been
worn by the piston rings to a slightly greater inside diameter than the
original inside diameter of the cylinder. In effect, this forms a small
but significant ridge within the cylinder extending from immediately above
the upper travel of the upper piston ring when the piston is at top dead
center to the top of the cylinder wall within the engine block.
When an engine is rebuilt to extend its life, the wearable bearing
components are replaced and this includes the connecting rod and
crankshaft bearings as well as the piston rings. In reassembling the
engine, the piston is removed and inserted through the top of the cylinder
head using various well known tools to compress the piston rings around
the piston and allow the piston to be slid into the cylinder. However,
operation of the engine would result in impact of the replaced piston ring
against the ridge that has been formed by the previous wear of the piston
rings within the cylinder. This impact in turn would damage or break the
top ring and bend or break the land on the piston and cause ultimately
catastrophic failure of the engine. In order to prevent this, it is
therefore necessary to ream the ridge out of the cylinder, typically by
the use of a ridge reamer. Unfortunately, the cylinder as originally
constructed in the engine block is provided with a slight taper at its
upper end so as to permit easy entry of the piston rings when inserted.
Reaming out the ridge provides a sharp corner at the upper end of the
cylinder wall in the engine block and this in turn can result in chipping
and breakage of piston rings which is undetected by the repair person
during insertion and can lead subsequently to failure.
The reaming process also requires special tools and a considerable amount
of skill in order to avoid reaming the ridge to other than a perfect
cylindrical shape which must be maintained to a high tolerance in order
that the replaced piston rings will form a gas tight seal.
If the cylinder is excessively reamed below the ridge, gas leakage or
blowby will occur. If the reaming does not maintain a high tolerance
cylindrical shape, the top ring could wedge and fracture the piston.
Insufficient reaming, on the other hand, may permit the top ring to make
contact with a portion of the ridge not removed, which could also cause
the top ring to wedge or fracture the piston.
SUMMARY OF THE INVENTION
It is the discovery of the inventor that the aforementioned problems
involved in reaming the ridge from the cylinder upon engine rebuilding and
piston ring replacement may be avoided by providing instead an eccentric
rod bearing for installation in the connecting rod at the crankshaft end.
This rod bearing as described below varies from the presently used
symmetrical rod bearing of the prior art by having a slightly greater
thickness along the lower section than on the upper section so as to
offset the bearing hole aperture provided for connecting the rod to the
crankshaft rod journal. This offset in a typical example reduces the
uptravel of the piston by 7/1000 of an inch (0.007), in effect lowering
piston Top Dead Center by this amount.
It has been found that by installing the eccentric rod bearings of the
invention that a piston with new piston rings is lowered a sufficient
distance below the level of the ridge previously formed in the cylinder,
that impact of piston ring and ridge never occurs. The engine can be
successfully operated with the replaced piston rings and the new rod
bearing without the necessity of reaming out the ridge remaining in the
cylinder.
This is particularly of use to amateur mechanics and do-it-yourself car
repair persons who then are able to rebuild and restore the efficiency of
a piston engine without having to learn the skills necessary to
successfully ream the ridges from the cylinder walls within the engine
block.
It is thus an object of the invention to provide a device which permits a
mechanic to rebuild a reciprocating internal combustion engine without the
necessity of reaming out ridge on the cylinder walls.
It is further an object of this invention to provide a device which permits
a mechanic of more limited skills to successfully rebuild an internal
combustion engine using limited tools and skill.
It is a further object of this invention to disclose a device which permits
the skilled shop mechanic to overhaul an engine in much less time and
therefore be able to charge less.
It is a further object of this invention to reduce the overhaul procedure
to engine disassembly, removing worn parts, replacing them with new ones,
and reassembly.
These and other objects of the invention will be more clearly seen from the
detailed description of the preferred embodiment which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view of a figurative piston, at top dead center, showing,
in cutaway view, piston rings within a worn cylinder, and the connecting
rod, inventive bearing and crankshaft.
FIG. 2 is a detailed section view of a figurative piston, showing top dead
center if a prior art bearing were installed without reaming, and in
contrast, top dead center after installation of the inventive bearing,
showing the reduced uptravel, equal to the offset of the bearing centers.
FIG. 3 is a view of the bearings of the invention, as provided as segments,
as ready for installation in the lower end of the connecting rod.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2, I show, as a component of a typical internal
combustion engine (not shown), a piston 2 fit within a cylinder 4 to
provide reciprocating motion, and sealed against the cylinder wall 6 by a
plurality of piston rings 8. These rings 8 are known to have varying
designs: the two upper piston rings are denoted compression rings 8a, and
are particularly designed to provide a gas tight seal in contact between
the piston 2 and the cylinder wall 6; the lower ring is known as an oil
control ring 8b and is designed especially to scavenge excessive oil from
the cylinder wall 6, preventing oil pumping into the combustion chamber.
A connecting rod 12 is connected for operative transfer of power from the
piston 2 to a crankshaft 24. Connecting rod 12 is pivotally connected at
an upper end 16 through a piston pin 18 to the piston 2 and is connected
pivotally at a lower end 20 through a crankshaft rod journal 22, offset
from the center line of rotation 25 of the crankshaft 24. As is known,
this structure provides for conversion of the reciprocating motion of the
piston 2 to rotary motion of the crankshaft 24.
Between the lower end 20 of the connecting rod 12 and the crankshaft rod
journal 22 is placed a rod bearing 26. This is an oil lubricated sleeve
bearing usually having a steel base coated with a layer of bearing
material. The rod bearing 26 is lubricated with a thin film of oil through
well known provided bearing lubrication holes, not shown here.
This rod bearing 26 receives the entire force of the engine cylinder power
stroke and is one of the high wear components within a reciprocating
engine. During combustion, cylinder pressure can exceed 400 pounds per
square inch in a typical gasoline engine; a diesel engine generates even
greater pressure. Since this pressure is exerted during the power
downstroke, wear is concentrated on the top side 26a of the rod bearing
26.
Referring to FIG. 2, it can be seen that during engine operation, the
compression ring 8a around the piston 2 does not travel all the way to the
top of the cylinder 4 as the piston 2 rises to the top dead center
position 28. As the engine is operated, compression ring 8a, through
friction, wears away that portion of the cylinder wall 6 upon which it
rides, leaving a ridge 30 near the top of the cylinder 4 which defines a
portion of the cylinder 4 of a lesser diameter than the worn portion. It
is known that the piston rings 8 are of a flexible construction so that
they will expand to fill the space between the piston 2 and the cylinder
wall 6, even as they wear.
These same forces that cause the compression ring 8a to wear away at the
cylinder wall 6 also act upon the compression ring 8a making this ring
narrow gradually through wear. Each piston ring 8 is retained between
groove lands 3 in piston 2. Groove lands 3 supports the top and bottom of
each piston ring 8 while allowing the ring to expand against the cylinder
wall 6. As the piston 2 changes direction during reciprocating motion in
the cylinder, it rocks from side to side; this causes the piston ring 8 to
move with respect to the groove lands 3, causing wear of the piston ring
8. For this reason the piston ring becomes thinner during wear.
A replacement ring 8 is thus of a thicker vertical dimension than the worn
ring 8 being replaced. As a result, operation of the engine with replaced
rod bearings 26 and piston rings 8 would cause the compression ring 8a to
impact upon the bottom of the ridge 34, figuratively shown in FIG. 2. This
will result in damage to the compression ring 8a and bending or breakage
of the groove lands 3 within which the ring 8a is inserted; this damage
will rapidly cause catastrophic failure of the piston ring 8 and piston 2
within the cylinder 4 during operation. As a result, piston ring
manufacturers uniformly direct that the ridge 30 be reamed out of the
cylinder 4 when piston rings are replaced.
Further, it is typical when rebuilding an engine that the rod bearings 26
are replaced at the same time the piston rings 8 are replaced, and in many
cases the main crankshaft bearings 38 are also replaced and renewed. The
cummulative effect of bearing wear on rod bearings 26 and crankshaft
bearings 38 lowers the uptravel of the piston (which is against pressure),
thus lowering Top dead Center 28. Replacemant of these bearings removes
this wear, raising the uptravel or Top Dead Center, and this further
increases the need for removal of the ridge 30.
The process of reaming the ridge 30 is tedious and time consuming even for
a skilled mechanic with high quality tools. A novice mechanic, or a person
who only occasionally works on an engine may find it too difficult to
successfully complete. The instructions for operating a ridge reamer place
a great burden upon the skill and knowledge of the user. The user is
warned not to excessively ream the cylinder 4 and not to ream beyond a
certain depth as such will damage the cylinder walls 6 rendering the
engine useless. If, as is usual for casual mechanics, the engine is not
completely pulled from the vehicle during this process, it is very
difficult to successfully ream those cylinders 4 which are close to engine
obstruction such as the firewall. Lack of access to these obstructed
cylinders 4 in turn may result in uneven cutting by the reamer and damage
to the cylinder 4.
Even when the cylinder 4 is correctly reamed, the reaming process removes
the bevel 7 originally placed by the manufacturer at the entrance to the
cylinder 4 leaving a sharp corner at the upper end of the cylinder 4. This
sharp corner makes it very difficult to install rings 8 into the cylinder
4. While it is known that rings 8 are compressed within a ring compressor
to allow the piston 2 to be started into the cylinder 4, the piston must
be slid from the compressed sleeve into the cylinder 4. A novice mechanic
is very likely to chip or break a ring 8 when attempting this insertion
into a sharp cornered cylinder.
The invention eliminates these problems by providing an eccentric rod
bearing 26 which makes removal of the ridge 30 unnecessary. The inventive
rod bearing is constructed in two facing segments 27a,27b, each having two
bearing surfaces: an inner bearing surface 52 and an outer bearing surface
54, both formed so that, when segments 27a and 27b are joined each of the
two bearing surfaces form a substantially cylindrical shape. Outer bearing
surface 54 forms a cylindrical shape which has an outer circular diameter
42 equal to the diameter 42a of the aperture of the connecting rod 12
retaining the bearing 26. Inner bearing surface 52 forms a cylindrical
shape which has an inner diameter 46 slightly larger than the diameter of
crankshaft rod journal 22, to permit adequate oil flow for lubrication.
However, the center, or axis, 48 of the inner bearing surface 52, which is
the same as the center of the crankshaft rod journal 22, is offset by an
offset distance 51 from the center, or axis, 50 of the outer bearing
surface 54, which is the same as an imaginary center about which the lower
end 20 of the connecting rod 12 pivots. This offset distance 51, in one
typical example 0.007 (seven thousandths) of an inch, restricts the
uptravel of the rod 12 and piston 2 by the amount of the offset distance
51.
This offset distance 51 is depicted in exaggerated scale in the figures for
illustration. It is equivalent to making the lower segment 27a thicker
than the upper segment 27b by the offset distance 51, although it is clear
to those skilled in the art that the thickness of the segments 27a,27b
would be continuously variable, and the offset distance 51 would be the
difference of thickness at a point of maximum thickness in lower segment
27a opposite a point of minimum thickness in upper segment 27b.
Insert rod bearings 26 are normally built as two semicircular segments,
equipped with small lugs 56 which are recessed into grooves within the
connecting rod 12 and the connecting rod cap 44. These lugs prevent the
rod bearing 26 from turning in the bearing aperture of the connecting rod
12, once the rod cap 44 is secured in place.
The eccentric rod bearing 26 of the invention is thus built of two
segments, having differing thicknesses so as to create offset distance 51
between the centers 48,50. Alignment of the two pieces so as to form the
eccentric rod bearing 26 within the connecting rod 12 is easily
accomplished, as the lugs 56 provide sufficient alignment positioning. The
center line offset 51 may be accurately maintained with respect to the
connecting rod 12.
Offset 51 restricts the uptravel of the piston, lowering top dead center 28
by an equal amount from the top dead center 28 which would have existed
had rod bearing 26 been replaced with a new prior art rod bearing, as
shown in FIG. 2. Offset 51 also increases the downstroke or lower position
of the piston 2 by the same amount. However, the oil control ring 8b or
bottom ring is well lubricated and operates at a much lower temperature
than the compression ring 8b; thus the oil control ring 8b does not form a
significant ridge. Any ridge that may tend to form is worn away by piston
friction leaving a slight wavy effect, and any impact during the
downstroke is not deleterious.
As an example, a 200 cubic inch reciprocating gasoline engine that had been
operated for 127,000 miles was rebuilt. It was found that the installation
of new piston rings, new main bearings and a new standard rod bearing of
the prior art increased the top dead center or uptravel of the new
compression ring by four point five thousands (0.0045) of an inch.
Eccentric rod bearings of the design having centers offset (51) by 0.007
of an inch were installed. Upon starting of the engine there was no noise
or other indication that the new compression ring 8a was making contact
with the ridge 30. After two hours of operating the engine at varying
speeds, the pistons 2 were removed and inspected. There were no
indications that the compression ring 8a had made any contact with the
ridge 30.
That piston 2 had a reduced uptravel of 0.007 of an inch did not materially
affect the operation of the engine after rebuilding. In this context it
should be noted that normal replacement of the factory installed original
issue head gasket with a standard replacement gasket, as distributed in
the automotive after market, results in a markedly larger change of head
space; after compression, the factory gasket measured 0.022 inch thick
while the replacement gasket measured 0.057 inch, an increase in headspace
equivalent to reducing top dead center 28 of the piston 2 by 0.025 inch.
Thus standard rebuilding practices result in a change in the effective
internal piston compression within a cylinder over four times as great as
installation of the eccentric rod bearing 26, without a noticeable
degradation in engine performance.
Prior to overhaul, compression was measured in each of the six cylinders.
The average pressure was 132 psi before overhaul; The lowest measurement
was 128 psi. After overhaul and installation of the new bearing, the
engine was run for 2,000 miles and the compression check was made again.
Compression readings showed the average pressure to be 153 psi; the lowest
reading was 150 psi. These pressures are considered to be in the normal
range of a new engine. Application of the eccentric rod bearing does not
appear to cause a recordable effect on cylinder compression.
In a second example, a thin coat of metal blue was applied on the interior
of a cylinder 4 on and adjacent to the ridge 30. The engine was then
reassembled and run, the spark plug wire being removed from the measured
cylinder 4. The pistons were again removed and it was found that the metal
blue had been worn upward near the ridge 30 but not to the base 34 of the
ridge. Approximately 0.0025 inches of space were observed still coated
with metal blue beneath the ridge 30 indicating sufficient clearance of
the ridge by the new compression ring 8a.
After these two tests, the engine with the eccentric rod bearing was then
reassembled and operated for 56,000 miles. No change in gas mileage and
oil consumption could be detected.
It can thus be seen that the bearing 26 of the invention permits an engine
to be reassembled, and piston rings to be replaced without requiring the
mechanic to ream out the ridge in the cylinder.
It will of course be apparent that the offset within a given eccentric rod
bearing will have to be designed specifically for a given size of engine,
but from the example shown, the amount of offset should be readily
determinable by a skilled designer in the art for bearings for the after
market trade.
A specific example has been shown in the detailed description above but it
should be apparent that the invention extends to the more generic device
as claimed.
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